Abstract

Background

Sponges (Porifera) are nerve- and muscleless metazoa, but display coordinated motor
reactions. Therefore, they represent a valuable phylum to investigate coordination
systems, which evolved in a hypothetical Urmetazoon prior to the central nervous system
(CNS) of later metazoa. We have chosen the contractile and locomotive species Tethya wilhelma (Demospongiae, Hadromerida) as a model system for our research, using quantitative
analysis based on digital time lapse imaging. In order to evaluate candidate coordination
pathways, we extracorporeally tested a number of chemical messengers, agonists and
antagonists known from chemical signalling pathways in animals with CNS.

Results

Sponge body contraction of T. wilhelma was induced by caffeine, glycine, serotonine, nitric oxide (NO) and extracellular
cyclic adenosine monophosphate (cAMP). The induction by glycine and cAMP followed
patterns varying from other substances. Induction by cAMP was delayed, while glycine
lead to a bi-phasic contraction response. The frequency of the endogenous contraction
rhythm of T. wilhelma was significantly decreased by adrenaline and NO, with the same tendency for cAMP
and acetylcholine. In contrast, caffeine and glycine increased the contraction frequency.
The endogenous rhythm appeared irregular during application of caffeine, adrenaline,
NO and cAMP. Caffeine, glycine and NO attenuated the contraction amplitude. All effects
on the endogenous rhythm were neutralised by the washout of the substances from the
experimental reactor system.

Conclusion

Our study demonstrates that a number of chemical messengers, agonists and antagonists
induce contraction and/or modulate the endogenous contraction rhythm and amplitude
of our nerveless model metazoon T. wilhelma. We conclude that a relatively complex system of chemical messengers regulates the
contraction behaviour through auto- and paracrine signalling, which is presented in
a hypothetical model. We assume that adrenergic, adenosynergic and glycinergic pathways,
as well as pathways based on NO and extracellular cAMP are candidates for the regulation
and timing of the endogenous contraction rhythm within pacemaker cells, while GABA,
glutamate and serotonine are candidates for the direct coordination of the contractile
cells.